This invention relates generally to the field of medical diagnosis and more specifically to an apparatus for measuring anatomic angles. There are many health professionals involved in the care and treatment of patients with musculoskeletal injuries and diseases. These include Orthopedic Surgeons, Physiatrists, Rheumatologists, Physical Therapists, Physical Therapy Assistants, Physician's Assistants, Athletic Trainers, Personal Trainers, etc. Almost all of these health Professionals use goniometers. A goniometer, or protractor, is an instrument to measure angles. Specifically, when used for musculoskeletal problems, the goniometer has two arms extending from a pivot point. Angular degrees are marked around this pivot, or center of rotation. These musculoskeletal specialists use goniometers to measure joint angles, ranges of joint motion, and other angular measurements, such as angles of limb alignment (“bow legs” and “knock knees”), and the quadriceps angle (Q angle). The anatomic Q angle is the complementary angle of the angle measured from the Anterior Superior Iliac Spine (ASIS) at the front of the pelvis to the center of the Patella (kneecap) to the Tibial Tubercle (the bump on the front of the knee below the kneecap).
These health professionals commonly use an inexpensive short (7-8 inch), light, plastic goniometer, which is very handy and convenient to carry in a pocket. However, its small arms fail to provide accurate measurements for the large joints (shoulder, elbow, wrist, hip, knee, and ankle) where the bony landmarks can be 18 inches from the apex. Furthermore, when it is used as a protractor to measure the Q angle, the long distance between the ASIS (the prominent bone on each side of the front of the pelvis) and the patella or kneecap, which can be as much as 24 inches away, makes accuracy impossible.
Physical Therapists and their assistants, who frequently require accurate, serial angular joint measurements, solve this problem by using the somewhat more accurate, larger, but more awkward, long-armed 14-inch goniometers. These are most frequently made of metal or plastic. Physicians and others, who do not require very accurate measurement of joint angles, almost always rely solely on the small pocket goniometers. However, accurate measurements are required for the care and treatment of angular knee deformities: genu varum (bow legs) and genu valgum (knock knees). For more accurate measurement of these deformities orthopedic surgeons have turned to plain x-rays. However, this small goniometer supplies inaccurate estimates for the Q angle. Studies have proven that Physicians and Surgeons need accurate measurements of the Q angle for proper diagnosis and treatment of the most frequent knee complaint: anterior knee pain and related conditions such as patellar dislocations. About 15 years ago, because Q angle measurements were so inaccurate, and because plain x-rays cannot be used to measure the Q angle, many studies began to advocate using a measuring technique based on a Magnetic Resonance Image (MRI). This certainly improves the accuracy, but at a huge increase in cost. One MRI of the knee can cost between $3936 and $1044, at least in Northern California.
Many years ago the Lafayette Instrument Company produced a goniometer with extendable and contractible arms, but for a variety of reasons it did not prove to be popular or useful.
For many decades, the most popular and common instrument to be used for measurement of anatomic angles has been the small (approximately 8″×2″×0.125″), inexpensive, plastic, pocket goniometers/protractor. For those health professionals who desire greater accuracy, plastic goniometers are available in various sizes up to those with arms of 14 inches in length. Goniometers of similar and varied sizes are also available made of metal, which can be sterilized with high-pressure steam for use during surgery. One goniometer/protractor for measuring anatomic angles, which has extendable and retractable arms, has been manufactured by Lafayette Instrument Company, Inc.; however, this goniometer cannot be steam-sterilized for use in the operating room during surgery.
All of these prior goniometers have deficiencies that limit their usefulness. The most popular, small, inexpensive, pocket goniometer lacks accuracy for measuring anatomic angles when the anatomic landmark or landmarks are at a distance greater than 8 inches from the apex or pivot point of the goniometer; the greater the distance, the greater the error.
The large 14-inch goniometers are bulky, awkward, and not easily portable. They also lose accuracy when the anatomic landmark or landmarks are at a distance of greater than 14 inches from the apex or pivot point of the goniometer; again, the greater the distance, the greater the error.
The goniometer/protractor with extendable and retractable arms manufactured by Lafayette Instrument Co., Inc. has several deficiencies. It's length of 8 inches improves its portability, however its width of 2½ inches and thickness of more than 2¾ of an inch makes it too bulky to carry in a pocket easily. Its weight of 4 ounces is more than four times heavier than the popular small pocket goniometers, again decreasing portability. It uses a small magnifying glass mounted on one arm to read the degree marks mounted on the other, however this small magnifying window does not let in sufficient light to allow easy observation in a lowlight environment. Finally, its cost to manufacture is so high that it is approximately 20 times more expensive than the common small pocket goniometers. These deficiencies apparently account for the fact that it is rarely used in clinical practice.